A transflective display is a type of display which can be used in both transmissive and reflective modes. In transmissive mode, a backlight is provided which is used to illuminate the display. In the reflective mode, the ambient light is used to illuminate the display. A combination of these two provides the advantage that in areas of low illumination, the transmissive mode can be used, while when there is sufficient light, the reflective mode can be used, which helps in reducing the energy consumption.
FIG. 1 illustrates the cross section of a prior art transflective display system 199. Polarizers 103, 106 are placed in such a way that their transmission axes are aligned at 90 degrees with respect to each other. Polarizers 103, 106, also referred to as crossed polarizers henceforth, and liquid crystal 105 form a light valve. A light valve is a light modulator with controllable transmittance. The display uses a partial mirror 102 which is placed between the bottom polarizer 103 and the backlight 101. Color filter 104 is placed between polarizer 103 and liquid crystal 105. Mirror 109 is placed behind the backlight 101. The display works in transmissive and reflective modes.
The partial mirror 102 may be a mirror with holes. Alternately, partial mirror 102 may be a transflector. A transflector is an optical sheet designed to reflect as much light as possible incident from one face and to transmit as much light as possible incident from the other face. The transflector may be scattering in nature, to help even illumination.
Prior art systems are inefficient in transmissive and reflective modes. In system 199, in the transmissive mode, backlight 101 emits light 108. Part of light 108 passes through the partial mirror 102 and illuminates the display. The remaining part gets reflected back from the partial mirror. Light reflected back from the partial mirror is not recycled efficiently. Thus the display is inefficient in the transmissive mode. In the reflective mode, ambient light 107 gets reflected from the partial mirror 102 and illuminates the display. However, part of ambient light 107 passes through the partial mirror. Light which passes through the partial mirror is not recycled efficiently. Thus the display is inefficient in the reflective mode.